The present invention relates to a bipolar battery and a related method, and more particularly to a bipolar-battery and a related method utilizing polymer gel electrolyte having a higher ionic conductivity than polymer solid electrolyte.
It has been recently and earnestly desired to reduce exhausted amounts of carbon dioxide, for environmental-protection. In the vehicle industry, it has been expected to reduce exhausted amounts of carbon dioxide such as by introducing electric vehicles (EVs) and hybrid electric vehicles (HEVs), and there has been thus earnestly conducted development of secondary batteries for driving the motors of such vehicles, as decisive points for bringing these vehicles into practical use. Concerning secondary batteries, attention has been directed to so-called lithium-ion secondary batteries capable of achieving higher energy and higher output densities. Only, it is required to use series-connected multiple secondary batteries upon applying such secondary batteries to vehicles, so as to ensure larger outputs.
However, there is a tendency of lowered outputs in case of connecting the batteries via connecting portions, due to electrical resistance of the connecting portions. Further, batteries having connecting portions tend to exhibit deteriorated spatial efficiencies. Namely, the output densities, energy densities and the like of the batteries tend to be reduced due to the connecting portions.
In view of these circumstances, there have been developed bipolar batteries including current-collectors, each current-collector being provided with a positive-electrode-aimed active material (positive active material) and a negative-electrode-aimed active material (negative active material) at one and the other sides of the current-collector, respectively.
Japanese Patent Application Laid-open Publication No. 2000-100471 discloses a bipolar battery utilizing, as electrolyte, polymer solid electrolyte including no solution. This intends to provide a bipolar battery with a higher reliability and without anxieties of liquid leakage, gas generation and the like, by virtue of the absence of solution (electrolytic solution) in the battery. However, the polymer solid electrolyte has a lower ionic conductivity as compared with those electrolytes including separators impregnated with electrolytic solution, i.e., solution electrolytes, and compared with gel electrolytes, so that the polymer solid electrolyte has limitations in its output density, energy density and the like, thereby resulting in the present state waiting for a further improvement of ionic conductivity of polymer solid electrolyte so as to reach the practical stage.
Japanese Patent Application Laid-open Publication No. H11-204136 discloses a bipolar battery utilizing an electrolyte including electrolytic solution. This intends to provide the bipolar battery closest to the practical stage, because it is possible to obtain an improved ionic conductivity as well as a higher output density and a higher energy density of the battery, upon utilizing the electrolytic-solution-including electrolyte, particularly the gel electrolyte.